This SBIR grant application is to develop an optical ultrasound monitor (OUM) for the continuous and accurate assessment of plasma protein concentration (PPC), hematocrit and total protein concentration (TPC) of blood in patients undergoing hemodialysis. Current systems capable of measuring hematocrit require improvement in their sensitivity. The systems or procedures to measure both hematocrit and PPC are not suitable for clinical usages. The first phase of research and development is: 1)to incorporate an innovative calibration protocol from which the PI will utilize the sensitivity of the ultrasound density monitor to enhance that of the optical hematocrit monitor, thus enabling the OUM to measure accurately changes in hematocrit and PPC; 2) to demonstrate the accuracy of the OUM for assessing plasma and blood volume through a saline infusion protocol and the use of changes in hematocrit and PPC for assessing plasma volume change and microvascular blood pooling. During the course of hemodialysis, many patients develop hypotension and/or low cardiac output. Knowledge on how these deficiencies develop and what appropriate counter measures could be taken is limited. The monitoring of PPC and hematocrit will provide a basis for physicians and researchers: 1) to assess factors such as plasma volume change and microvascular pooling in effecting cardiac filling and subsequently the development of hypotension during hemodialysis; 2) to develop a blood volume control strategy to alleviate symptoms during dialysis; 3) to improve the effectiveness of hemodialysis in removing excess fluid from the body tissue. PROPOSED COMMERCIAL APPLICATION: NOT AVAILABLE